To meet the increased demand for polyetherimide, the “displacement polymerization” process has been developed. Synthesis of polyetherimides via the displacement polymerization process includes imidization as described, for example, in U.S. Pat. No. 6,235,866), to produce a bisphthalimide substituted with a leaving group; synthesis of a salt of a dihydroxy aromatic compound, as described, for example, in U.S. Pat. No. 4,520,204; and polymerization by reacting the substituted bisphthalimide and the salt (“displacement”), as described, for example, in U.S. Pat. No. 6,265,521, followed by downstream activities.
In particular, imidization generally proceeds by reaction of 2 moles of a phthalic anhydride substituted with a leaving group with 1 mole of diamine in a reaction solvent, such as ortho-dichlorobenzene (ODCB) to provide a bis(phthalimide) substituted with two leaving groups. In a specific embodiment, the substituted phthalic anhydride is 4-chlorophthalic anhydride, the diamine is meta-phenylene diamine, and the bisphthalimide is a bis(chlorophthalimide) (ClPAMI). When 3-chlorophthalic anhydride (3-ClPA) and 4,4-diaminodiphenyl sulfone (DDS) are used, the product is 4,4′-bis(phenyl-3-chlorophthalimide)sulfone (DDS ClPAMI)). The bis(phthalimide) polymerizes with bisphenol A disodium salt (BPANa2) to provide the polyetherimide via chloro-displacement in the presence of a phase transfer catalyst, such as hexaethylguanidinium chloride.
There nonetheless remains an ongoing, unmet need for polyetherimides having improved color properties, and methods of making such polyetherimides.